A discontinuity in an electrical circuit path or lead can result from a break in the lead, a faulty connection, a faulty component, and the like. The result is an open circuit that will not conduct current and, hence, a failure in the apparatus in which the circuit path is connected.
Constant voltage power supplies are designed to maintain a constant voltage to a load that may be located some distance (for example, tens of feet) from the power supply. To maintain a constant voltage at the load, the design must consider a number of concerns, including the voltage drop across the length of wire between the power supply and the load, and current demands of the load itself.
A design that accommodates these concerns employs one or more sense leads connected to the load and connected in a feedback control loop. The voltage at the load is fed back via the sense leads for comparison to a reference voltage. A difference voltage determined as a result of the comparison enables generation of an error signal that is used to adjust the voltage output of the power supply to achieve and maintain the voltage delivered to the load constant. A break or open circuit in the sense leads prevents the power supply from delivering a constant voltage to the load and may even result in an overvoltage condition that damages the load.
To prevent an overvoltage, a prior art scheme involves the connection of sense protect resistors between the sense leads and the local output leads of the power supply. However, this scheme does not detect a discontinuity in a sense lead. Although the sense protect resistors prevent the overvoltage situation, an undetected discontinuity in a sense lead will cause the power supply's output voltage to change and to have poor voltage regulation.
Some prior solutions to the continuity checking problem have used complicated schemes to separately measure the resistance between a positive sense lead and the positive output lead, and between the negative sense lead and the negative output lead. These solutions have involved the use of costly measuring devices or labor intensive procedures.
Accordingly there is a need for a constant voltage power supply having a circuit that checks for continuity in the sense leads of the power supply. In particular, there is a need for such a circuit that allows checking of the sense lead status before enabling the output of the power supply, so as to prevent possible overvoltage damage to a load.